If cars and mobile phones are both consumer goods, how come cars are more likely sold by model year than mobile phones?

Untrue. Mobile phones are WAY more likely to be purchased than a brand new car. The reason being that most celluar phones cheaper than any car being sold

True. Because safety is associated with the car model year whereas in the case of mobiles tendency is to go for the most practical choice which sometimes is not necessarily the latest model but one that simply attracts esthetically, has a reasonable price and offers basic commands e.g. allows phone calls roaming and photographs (the function varying on preference).

I only have an old banger, and my mob phone is getting close to fitting into that category too. ;-)

It's just the way different categories sort out.